Cement render system

ABSTRACT

A method for applying render to a substrate, said method including the steps of: securing a layer of confining mesh having a three-dimensional open cellular structure to the substrate; applying a base layer of cementitious material over the confining mesh; and screening the base layer to a depth at least substantially level with an outer surface of the confining mesh. Preferably, the method includes the further step of: applying a layer of reinforcing mesh over the base layer; and applying a top coat of cementitious material over the reinforcing mesh. A cementitious plaster formulation for use in the method as defined in the method according to any one of claims  1  to  25 , said formulation including: 10% to around 40% cement by weight of total dry ingredients; 50% to around 85% sand by weight of total dry ingredients; 5% to around 40% fly ash by weight of total dry ingredients; an air entraining agent and a thickener respectively combined in a ratio of from 1:1 to around 120:1 and in a combined amount of between 0.01% and around 10% by weight based on the weight of the cement; and sufficient water to provide suitable fluidity.

FIELD OF THE INVENTION

[0001] The present invention relates to a method for applying render toa surface, and to a cementitious formulation for use in the method.

[0002] The invention has been developed primarily for use in thebuilding industry, and more particularly in housing construction. Theinvention will therefore be described predominantly in this context. Itwill be appreciated, however, that the invention is not limited to thisfield of use.

BACKGROUND OF THE INVENTION

[0003] Various techniques for applying render to a substrate are known.One of the more common techniques used in housing construction isreferred to as “stucco”. This technique makes use of a flat wirereinforcing mesh to facilitate the building up of a solid cladding layerof cementitious plaster over a barking material, which is typicallyfixed to a light timber or steel frame. The cementitious plaster isusually applied either by hand, or more commonly in recent times bymeans of shot-crete spraying, in consecutive layers or coats, until thedesired cumulative thickness has been achieved. This thickness istypically between 20 and 25 mm. The system has a number of advantagesincluding that it can be formed in a variety of shapes around complexcurves, it can be finished in a range of surface textures, and it canprovide a solid uniform appearance with adequate impact resistance.However, the conventional stucco render system is also subject to anumber of inherent disadvantages.

[0004] Firstly, in order to build the sprayed stucco plaster to therequired thickness, it must be applied in a multiple of relatively thinlayers so as to avoid sagging and wastage. This creates planes ofweakness in the render system at the interfaces between the layers,which, if incorrectly applied and treated, can induce cracking, andbonding failures. In the past, this problem has been addressed by theapplication of a curing agent to the plaster composition. The curingagent is typically sprayed onto the surface of each layer as a film.Because of the water loss at the surface of the plaster, the curingagent must be applied within a relatively short time from when theplaster is sprayed, typically within 15 to 20 minutes. Then, before afurther plaster layer can be added, the curing agent must be removed.Otherwise, it can prevent or impede adequate bonding between adjacentlayers of the plaster composition. These steps all contribute to thematerial cost, the time involved, and the expertise required in order toimplement the system effectively. The process is also highlyspecialised, and is susceptible to inconsistent application and operatorerror.

[0005] A further disadvantage is that stucco plaster normally comprisesa mix of cement, sand and lime, which is difficult to pump and sprayeffectively by shot-creting as a wet mix. Accordingly, the operator isusually limited to the use of a day mix formulation. However, theapplication process then becomes heavily reliant upon the skill of theoperator to estimate the appropriate level of water which must be addedto the mix “on the fly”, during spraying. This in turn introduces asignificant potential for variability in the mix composition, which mayinfluence its shrinkage and crack resistance characteristics, and maythereby adversely affect the durability of the render system.

[0006] In an attempt to address this problem, it is known to usemodified cement and sand plaster mixes, which are designed to be appliedusing the more consistent wet mix shot-creting technique. However, suchmixtures are difficult to use in high build (i.e. high depth)applications requiring a conventional sand and cement render finish.This is because the presence of modifying polymers in the mix makes ittoo runny to build to more than about 8 to 10 mm in thickness withoutthe aid of an accelerator. Then, once applied, the accelerated mixbecomes too sticky and hard to sponge finish. Consequently, additionaldecorative texture coatings are required in order to provide the desiredsponge finished appearance, which adds further to the time and costinvolved in the process overall.

[0007] Additional disadvantages include the fact that the conventionalstucco system requires highly skilled plasterer in order to achieve aconsistent high quality flat finish. Such operators are in limitedsupply, and are expensive. The system is also prone to shrinkagecracking and surface peeling, particularly when drying in exposedconditions. Furthermore, the system requires lengthy and hence costlywaiting times between coats to enable each layer of plaster to hydrateand gain full strength. This requirement is often complicated andprotracted by adverse weather conditions and limited site access,thereby further compromising the practical and commercial viability ofthe system in an increasingly competitive housing market.

[0008] It is an object of the present invention to overcome orameliorate one or more of the disadvantages of the prior art, or atleast to provide a useful alternative.

DISCLOSURE OF THE INVENTION

[0009] Accordingly, in a first aspect, the invention provides a methodfor applying render to a substrate, said method including the steps of:

[0010] securing a layer of confining mesh having a three-dimensionalopen cellular structure to the substrate;

[0011] applying a base layer of cementitious material over the confiningmesh;

[0012] sereeding the base layer to a depth at least substantially levelwith an outer surface of the confining mesh;

[0013] applying a layer of reinforcing mesh over the base layer; and

[0014] applying a top coat of cementitious material over the reinforcingmesh.

[0015] Preferably, the confining mesh is formed from a plasticsmaterial, ideally a high density polyethylene plastic. In the preferredembodiment, the confining mesh is initially provided in a collapsedconfiguration and is selectively expandable prior to use into athree-dimensional open celled honeycomb structure, with the size of thecells being adjustably determined by the extent of expansion. The depthof the cellular structure is preferably between 5 mm and around 100 mm,more preferably between 10 mm and around 60 mm, and ideally between 15mm and around 25 mm.

[0016] The cementitious material of the base layer is preferably appliedby shot-crete spraying onto the confining mesh so as substantially tofill the cellular structure in a single application, and then screededto a depth approximately level with the outer surface of the confiningmesh. Preferably, upon drying, the cellular walls of the confining meshact as expansion joints for the cementitious material to resistshrinkage cracking.

[0017] Preferably, the cementitious material for the base layer isformed from a polymer modified sand and cement plaster composition.Preferably, the plaster composition includes a combination of cement,sand, fly ash, at least one air entraining agent, at least onethickening agent, and sufficient water to provide suitable fluidity.Preferably, the air entraining agent and the thickener are combinedrespectively in a weight ratio of between 1:1 and 120:1, and in acombined amount of 0.01% to 10% by weight based on the weight of thecement.

[0018] Preferably, the reinforcing mesh is formed from glass fibre,which is preferably embedded in the surface of the base layerimmediately after spraying.

[0019] Preferably, the top coat is formed from a cementitious material,substantially the same in composition as the base layer. The top coat ispreferably also applied by spraying, preferably to a depth of between 1mm and around 20 mm, more preferably between 2 mm and around 10 mm, andideally between 4 mm and around 6 mm. The top coat is preferablyscreeded level and optionally sponge finished to provide a surfacetexture similar to conventional stucco render.

[0020] In the preferred embodiment, the method includes the further stepof applying a relatively thin finishing layer over the top coat.Preferably, the finishing layer includes one, and ideally at least twocoats of a high build acrylic membrane decorative paint. The paint mayideally be applied by brushing, rolling or spraying over the top coat.

[0021] According to a second aspect, the invention provides acementitious plaster formulation for use in the method as describedabove, said formulation including:

[0022] 10% to around 40% cement by weight of total dry ingredients;

[0023] 50% to around 85% sand by weight of total dry ingredients;

[0024] 5% to around 40% fly ash by weight of total dry ingredients;

[0025] an air entraining agent and a thickener respectively combined ina ratio of from 1:1 to around 120:1 and in a combined amount of between0.01% and around 10% by weight based on the weight of the cement; and

[0026] sufficient water to provide suitable fluidity.

[0027] Preferably, the proportion of cement in the composition isbetween 13% and around 35%, and ideally between 15% and around 30% byweight of the total dry ingredients.

[0028] Preferably also, the proportion of sand in the composition isbetween 60% and around 80%, and ideally between 65% and around 70% byweight, based on the total dry ingredients.

[0029] The proportion of fly ash comprising particles of less than 45microns and greater than 10 microns in size in the composition ispreferably between 5% and around 40%, more preferably between 10% andaround 35%, and most preferably between 15% and around 30% by weight,based on the total dry ingredients.

[0030] The proportion of fly ash comprising particles of less than 10microns in size in the composition is preferably between 1% and around25%, more preferably between 5% and around 20% and most preferablybetween 10% and around 15% by weight, based on the total dryingredients.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] A preferred embodiment of the invention will now be described, byway of example only, with reference to the accompanying drawings inwhich:

[0032]FIG. 1 is a cutaway perspective view showing a substrate renderedin accordance with the method of the present invention.

[0033]FIG. 2 is an enlarged perspective view showing the open cellularconfiguration of the confining mesh in the expanded configuration; and

[0034]FIG. 3 is a plan view of the confining mesh in the expandedconfiguration.

PREFERRED EMEBODIMENTS OF THE INVENTION

[0035] Referring to the drawings, the invention provides a method forapplying render 1 to a substrate 2. In the context of housingconstruction, the substrate can be plywood, fibre insulating board,fibre reinforced cement (FRC) sheet, polystyrene, weatherboard, gyprock,brick, hollow core blocks, or other suitable rigid or semi-rigidmaterials, typically supported by a conventional timber or steel frame3.

[0036] The first step in the process involves the use of a layer ofconfining mesh 5, having an open, three-dimensional structure defining aseries of discrete cellular compartments 6, in the nature of a coarsehoneycomb structure. The mesh is formed from a plastics material,ideally a high density polyethylene (HDPE). It is initially provided ina collapsed configuration (not shown) which is selectively expandedprior to use into the three dimensional open celled structureillustrated (see FIGS. 2 and 3), with the size and shape of the cellsbeing determined by the extent of biaxial expansion. The depth of thecellular structure is selected according to the architectural andstructural nature of the building, the desired aesthetics, desiredthermal and acoustic insulation characteristics, cost considerations,and other factors. Within these constraints, however, the depth ispreferably between 5 mm and around 100 mm, more preferably between 10 mmand around 60 mm, and ideally between 15 mm and around 25 mm.

[0037] The mesh material is typically delivered to site in the form ofcollapsed strips 60 mm wide by 15 mm deep by 2400 mm long, which expandto form diamond shaped cells. With the mesh expanded to the desiredextent, it is secured to the substrate by staples, tacks, screws,adhesive, or other suitable means. The preferred fastening techniqueinvolves the use of staples or nails. One example of a suitable materialfor the confining mesh is sold under the name EnviroGrid™, by AGHIndustries, Inc., USA and is described in U.S. Pat. No. 4,797,026although it should be understood that this material was designed and isconventionally used for an entirely different purpose, in the context ofsoil stabilisation. It should also be appreciated that any othersuitable shape and form of mesh may be used. Furthermore, the mesh maybe formed from other materials such as metal foil, timber, cardboard,paper, woven fabric, reinforced composites, or other suitable plasticsmaterials. The mesh may also be applied in multiple layers, with eachlayer either being fastened to the underlying layer or supporteddirectly from the substrate. In this case, the cell size, shape,configuration and material composition may vary between layers.

[0038] With the confining mesh in place, the next step in the processinvolves the application, of a base layer 8 of cementitious plastermaterial. The specific formulation of cementitious plaster will bedescribed in more detail below. The cementitious composition is conveyedto the point of application by pumping, typically using a peristaltic ora mono pump, and is conveniently applied by spraying, using conventionalwet shot-creting techniques, as a single layer so as to fill andsubstantially cover the confining mesh. During the process, theconfining mesh prevents the cementitious plaster material from slumping,even at depths of 60 mm to 100 mm. The plaster is then screeded to adepth substantially level with or marginally covering the outer surfaceof the confining mesh.

[0039] In this way, the mesh segments and confines the cementitiousplaster material of the base layer of into a large number of contiguousbut discrete pockets. The mesh walls extending between the pocketseffectively then provide expansion joints for the plaster containedwithin the pockets, which relieve stresses caused by shrinkage duringthe hydration and drying process. Consequently, the problems typicallyassociated with shrinkage cracking are substantially ameliorated. At thesame time, the interconnections between the cell walls providereinforcing for the base layer to improve its structural integrity andimpact resistance. If necessary, the cell walls may be formed with aroughened texture to improve bonding with the cementitious plaster ofthe base layer. Such roughening may be achieved, for example, byimpregnating the plastics material of the mesh with a particulatematerial such as sand, adhering a particulate material such as sand tothe exposed surfaces of the mesh, applying a surface primer, rougheningthe surface through abrasion or chemical etching, or by other suitablemeans.

[0040] The next step in the process involves the application of a layerof reinforcing mesh 10 over the top of the base layer. Ideally, thereinforcing mesh is formed from woven or chopped fibreglass matting andis embedded into the surface of the base layer while the cementitiousmaterial is still wet. Additionally, or as an alternative to this step,the cementitious plaster of the base layer can itself be impregnatedwith reinforcing fibres formed, for example, from steel, glass,polypropylene, cellulose, or other suitable materials.

[0041] The next step involves the application of a top coat 12 ofcementitious material over the reinforcing mesh 10, such that thefibreglass reinforces the interface between the base layer and the topcoat (see FIG. 1). The top coat is ideally formed from a cementitiousmaterial, which is substantially the same in composition as the baselayer. It will be appreciated, however, that the material composition ofthe two layers need not be the same, provided they are sufficientlycompatible to ensure adequate bond strength with each other and with thereinforcing mesh, at the interface. The top coat 12 is again applied byshot-crete spraying, preferably to a depth of between 1 mm and around 20mm, more preferably between 2 mm and around 10 mm, and most preferablybetween 4 mm and around 6 mm. Once applied to the desired thickness, thetop coat is screeded level and finished to the desired surface texture.

[0042] In one particularly preferred form of the invention, the top coatis trowelled and sponged to provide a surface which is similar inappearance and texture to conventional stucco render. In this way, thetop coat is ready to paint, without the need for a supplementary texturecoating. This is possible partly by virtue of the fact that the plastercomposition (as described below) contains a significant volume of coarsesand fraction with a substantial proportion of particles being up toaround 600 microns in size. Such particles are normally absent inconventional polymer modified renders designed for sprayed plasterapplications, in which the sand fraction is normally composedsubstantially of silica flour, with particles averaging only around 30microns in size.

[0043] The final step in the process involves the application of afinishing layer 14 over the top coat 12. The finishing layer ideallyincludes at least two coats of a high build acrylic membrane decorativepaint, applied by brushing, rolling or spraying directly over the topcoat. Alternatively, however, it will be appreciated that a wide varietyof paints, membrane finishes or texture coatings, in a range ofthicknesses and combinations, may be applied using numerous applicationand finishing techniques. Such materials and techniques are well knownto those skilled in the art, and so will not be described in moredetail.

[0044] Turning now to describe the plaster formulation in more detail,the cementitious material ideally includes a composition of cement,sand, fly ash, at least one air entraining agent, at least onethickening agent, and sufficient water to provide suitable fluidity. Theair entraining agent and the thickener are respectively combined in aratio of from 1:1 to 120:1 and in a combined amount of 0.01% to around10% by weight, based on the weight of the cement.

[0045] The term “cement” in the context of this formulation is intendedto include, but is not limited to: hydraulic and alite cements, such asPortland Cement; blended cements such as Portland Cement blended withfly ash, blast furnace slag, pozzolans, and the like, and mixturesthereof; masonry cement; oil well cement; natural cement; aluminacement; expansive cements, and the like, and mixtures thereof. Theproportion of cement in the composition is preferably between 10% andaround 40%, more preferably between 13% and around 35%, and ideallybetween 15% and around 30% by weight of the total dry ingredients.

[0046] Any type of sand that is commonly used in the building industry,may be used effectively in the context of this invention. Examples ofsuitable sands include ASTM 20/30 silica sands, dune sands, beach sandsand job site sands. The proportion of sand in the composition ispreferably between 50% and around 85%, more preferably between 60% andaround 80%, and most preferably between 65% and around 70% by weight,based on the total dry ingredients.

[0047] The term “fly ash” generally refers to a solid powder having achemical composition similar to or substantially the same as thecomposition of the material that is produced during the combustion ofpowdered coal. This material typically comprises from 25% to about 60%silica, from 10% to about 30% AL₂O₃, from 5% to about 25% Fe₂O₃, from 0%to about 20% CaO, and from 0% to about 5% MgO. Fly ash particles aretypically spherical, ranging in diameter from 1 to 45 microns. In thecementitious composition, the proportion of fly ash comprising particlesof less than 45 microns and greater than 10 microns in size ispreferably between 5% and around 4% more preferably between 10% andaround 35%, and most preferably between 15% and around 30% by weight,based on the total dry ingredients. The proportion of fly ash comprisingparticles of less than 110 microns in size in the composition ispreferably between 1% and around 25%, more preferably between 5% andaround 20% and most preferably between 10% and around 15% by weight,based on the total dry ingredients.

[0048] Typical air entraining agents (AEAs) suitable for use in theinvention include: nonionic AEAs such as fatty alkanolamides,ethoxylated fatty amines, ethoxylated fatty acids, ethoxylatedtriglycerides, ethoxylated alkylphenols, ethoxylated alcohols, alkylethoxylates, alkylaryl ethoxylates; cationic AEAs such as amineethoxylates and amine oxides; amphoteric AEAs such as betaines; andanionic AEAs such as fatty alkyl ether sulfates, fatty alkylaryl ethersulfates, alkyl benzene sulfonates, alpha-olefinic-sulfonic acids orsalts thereof, sulfosuccinates, and fatty sulfonates. Suitable AEAs mustideally be soluble at a pH range of 3 to 6 in order to ensure solubilityin the cementitious mixture, and must ideally also be soluble at a pH of10 to 11 and above, in view of the hydration process taking place in themortar. Accordingly, the AEA ideally has a relatively wide solubilityrange.

[0049] Thickening agents suitable for use in the invention include oneor more polysaccharide plasticizers which can be further subdivided intocellulose based materials and derivatives thereof, starch basedmaterials and derivatives thereof, and other polysaccharides. Suitablecellulose based rheology-modifying agents include, for example,methylhydroxyethylcellulose, hydroxymethylethylcellulose,carboxymethylcellulose, methylcellulose, ethylcellulose,hydroxyethylcellulose, hydroxyethylpropylcellulose, etc. The entirerange of possible permutations is enormous and for practical purposesneed not be listed. Nevertheless, it will be appreciated that many othercellulose materials have essentially the same or similar properties asthose mentioned and are equivalent for the present purposes. Suitablestarch based materials include, for example, amylopectin, amylose,sea-gel, starch acetates, starch hydroxyethyl ethers, ionic starches,long-chain alkylstarches, dextrins, amine starches, phosphate starches,and dialdehyde starches. Other natural polysaccharide basedrheology-modifying agents include, for example, alginic acid,phycocolloids, agar, gum arabic, guar gum, welan gum, locust bean gum,gum karaya, and gum tragacanth.

[0050] Normally, polymer modified cement/sand plaster compositions aresubject to a number of inherent limitations which restrict the manner inwhich they can be used. Firstly, due to the presence of polymers neededto provide pumpability, sprayability and adherence to a backingmaterial, the mix becomes too sticky and saggy if used in high buildrender applications (i.e. greater than around 10 mm in thickness).Therefore, a number of thin layers are usually required in order toachieve the desired cumulative build thickness. Another reason for therelatively thin application is the need to control the setting timewhich is heavily retarded due to the presence of organic polymers in themodified mix. In addition, sand or silica flour (with a maximum sizefraction less than 250 microns) is normally used in the plastercomposition, rendering the mix low in the 300 to 600 micron coarse sandfraction needed to provide the appearance of a conventional spongefinish.

[0051] Surprisingly, the polymer modified mix composition of the presentinvention as described above exhibits an ability to set (i.e. reachfirmness) within 90 minutes of application, even in high build rendersituations. Furthermore, it is comparable in pumpability andsprayability to conventional polymer modified plaster compositions,while exhibiting an ability to be sponge finished for an appearancesimilar to conventional sand/cement plasters and stucco renders.

[0052] Confining meshes of the type described are known, but havetypically only been used for soil reinforcement and stabilisation. Theyhave not hitherto been used in the context of cement rendering. This isfirstly due to the relatively poor adhesion between cementitiousplasters and high density polyethylenes and similar materials, andsecondly because of the expected mismatch between the movement of thetwo materials when exposed to external environmental conditions.Surprisingly, however, it has been found that the use of this mesh inthe context of the present invention has resulted in a peel free andsubstantially crack resistant render system, due to the synergisticinteraction between the cementitious render of the base layer and theconfining mesh. Again unexpectedly, this compatibility has been achievedin part by embedding a layer of fibreglass reinforcing mesh over theplaster filled pockets of the confining mesh.

[0053] Overall, the invention therefore provides a number of unexpectedadvantages over conventional stucco and other rendering techniques. Itenables a relatively high build or thickness of render to be achieved ina single base coat, without the need for multiple layers and withoutslumping. It thus eliminates the waiting time between layers as well asthe need to apply a curing agent between layers to ensure adequatebonding. Additionally, the technique of spraying and screeding, in placeof hand plastering, means the application process is less specialisedand does not require operators to be skilled to the same degree. It isalso more consistent and less susceptible to operator error.

[0054] The system is not limited to the conventional stucco thickness ofaround 20 mm. Rather, a base layer with a thickness of more than 50 mmand up to 100 mm can be achieved simply by varying the depth of theconfining mesh. This particular feature enables the formation of athick-clad render system that is applicable to virtually any surface andyet is comparable to masonry in terms of feel, solidity, impactresistance and durability.

[0055] Because of the synergistic interaction between the mesh and thecementitious material of the base layer, there is improved resistance toshrinkage cracking and surface peeling during drying, which ultimatelyimproves the strength and longevity of the render system. At the sametime, the system provides a finished top coat which is ready to paintwithout the need for additional layers of surface texture material.

[0056] The system is comparable in pumpability and sprayability withknown polymer modified plaster compositions, yet sets quickly even inhigh build render situations, and allows sponge finishing to a texturesimilar to conventional stucco render, which is highly desirable incertain segments of the market.

[0057] The system may be used over substrates of concrete, masonry, corefilled sandwich walling, or other structural materials to improveaesthetics, thermal and acoustic insulation, weatherproofing, strength,and durability. It may also be applied to semi-rigid backing materialssuch as plywood, cellulose fibre insulating board, fibre reinforcedcement board, polystyrene, plasterboard, or other cladding materials asa masonry substitute for improved solidity, strength, insulation andaesthetics.

[0058] The application of the present invention in the building industryis thus far reaching and wide ranging, not just as an alternative rendersystem, but as an alternative method of building construction. In allthese respects, the invention represents a practical and commerciallysignificant improvement over the prior art.

[0059] Although the invention has been described with reference tospecific examples, it will be appreciated by those skilled in the artthat the invention may be embodied in many other forms.

1. A method for applying render to a substrate, said method includingthe steps of: securing a layer of confining mesh having athree-dimensional open cellular structure to the substrate; applying abase layer of cementitious material over the confining mesh; screedingthe base layer to a depth at least substantially level with an outersurface of the confining mesh; applying a layer of reinforcing mesh overthe base layer; and applying a top coat of cementitions material overthe reinforcing mesh.
 2. A method according to claim 1, wherein theconfining mesh is formed from a plastics material.
 3. A method accordingto claim 2, wherein the plastics material consists substantially of ahigh density polyethylene plastic.
 4. A method according to any one ofclaims 1 to 3, wherein the confining mesh is initially provided in acollapsed configuration and is selectively expandable prior to use intoa three-dimensional open cellular honeycomb structure, with the size ofthe cells being adjustably determined by the extent of expansion.
 5. Amethod according to claim 4, wherein the depth of the cellular structureis between 5 nm and around 100 mm.
 6. A method according to claim 5wherein the depth of the cellular structure is between 10 mm and around60 mm.
 7. A method according to claim 6, wherein the depth of thecellular structure is between 15 mm and around 25 mm.
 8. A methodaccording to any one of the preceding claims, wherein the methodincludes the steps of applying the cementitious material of the baselayer by shot-crete spraying onto the confining mesh so as substantiallyto fill the cellular structure in a single application, and subsequentlyscreeding the cementitious material to a depth approximately level withthe outer surface of the confining mesh.
 9. A method according to anyone of the preceding claims, wherein the confining mesh is composed andconfigured such that, during drying, the cellular walls act as expansionjoints for the cementitious material to resist shrinkage cracking.
 10. Amethod according to any one of the preceding claims, wherein thecementitious material for the base layer is formed from a polymermodified sand and cement plaster composition.
 11. A method according toclaim 10, wherein the plaster composition includes a combination ofcement, sand, fly ash, at least one air entraining agent, at least onethickening agent, and sufficient water to provide suitable fluidity. 12.A method according to claim 11, wherein the air entraining agent and thethickener are combined respectively in a weight ratio of between 1:1 andaround 120:1, and in a combined amount of between 0.01% and around 10%by weight based on the weight of the cement component. 13 A methodaccording to any one of the preceding claims, wherein the reinforcingmesh is formed from glass fibre.
 14. A method according to any one ofthe preceding claims, including the further step of embedding thereinforcing mesh in the surface of the base layer immediately afterapplication of the base layer.
 15. A method according to any one of thepreceding claims, wherein the top coat is formed from a cementitiousmaterial, substantially the same in composition as the base layer.
 16. Amethod according to any one of the preceding claims, wherein the topcoat is applied by spraying.
 17. A method according to any one of thepreceding claims, wherein the top coat is applied to a depth of between1 mm and around 20 mm.
 18. A method according to claim 17, wherein thetop coat is applied to a depth of between 2 mm and around 10 mm.
 19. Amethod according to claim 18, wherein the top coat is applied to a depthof between 4 mm and around 6 mm.
 20. A method according to any one ofthe preceding claims, including the further step of screeding the topcoat substantially level following the initial application.
 21. A methodaccording to claim 20, including the further step of sponge finishingthe top coat after screeding to provide a surface texture similar toconventional stucco render.
 22. A method according to any one of thepreceding claims, including the further step of applying a relativelythin finishing layer over the top coat.
 23. A method according to claim22, wherein the finishing layer includes at least one coat of adecorative paint.
 24. A method according to claim 23, wherein thefinishing layer is formed from a high build acrylic membrane paint. 25.A cementitious plaster formulation for use in the method as defined inthe method according to any one of claims 1 to 24, said formulationincluding: 10% to around 40% cement by weight of total dry ingredients;50% to around 85% sand by weight of total dry ingredients; 5% to around40% fly ash by weight of total dry ingredients; an air entraining agentand a thickener respectively combined in a ratio of from 1:1 to around120:1 and in a combined amount of between 0.01% and around 10% by weightbased on the weight of the cement; and sufficient water to providesuitable fluidity.
 26. A cementitious plaster formulation according toclaim 25, wherein the proportion of cement in the composition is between13% and around 35%.
 27. A cementitious plaster formulation according toclaim 26, wherein the proportion of cement in composition is between 15%and around 30% by weight of the total dry ingredients
 28. A cementitiousplaster formulation according to any one of claims 25 to 27, wherein theproportion of sand in the composition is between 60% and around 80%. 29.A cementitious plaster formulation according to claim 28, wherein theproportion of sand in the composition is between 65% and around 70% byweight, based on the total dry ingredients.
 30. A cementitious plasterformulation according to any one of claims 25 to 29, wherein theproportion of fly ash comprising particles of less than 45 microns andgreater than 10 microns in size in the composition is between 5% andaround 40% by weight, based on the total dry ingredients.
 31. Acementitious plaster formulation according to claim 30, wherein theproportion of fly ash comprising particles of less than 45 microns andgreater than 10 microns in size in the composition is between 10% andaround 35% by weight, based on the total dry ingredients.
 32. Acementitious plaster formulation according to claim 31, wherein theproportion of fly ash comprising particles of less than 45 microns andgreater than 10 microns in size in the composition is between 15% andaround 30% by weight, based on the total dry ingredients.
 33. Acementitious plaster formulation according to any one of claims 25 to32, wherein the proportion of fly ash comprising particles of less than10 microns in size in the composition is between 1% and around 25% byweight, based on the total dry ingredients.
 34. A cementitious plasterformulation according to claim 33, wherein the proportion of fly ashcomprising particles of less than 10 microns in size in the compositionis between 5% and around 20% by weight, based on the total dryingredients.
 35. A cementitious plaster formulation according to claim34, wherein the proportion of fly ash comprising particles of less than10 microns in size in the composition is between 10% and around 15% byweight, based on the total dry ingredients.
 36. A cementitious plasterformulation according to any one of claims 25 to 34, wherein the fly ashcomprises from 25% to about 60% silica, from 10% to about 30% AL₂O₃,from 5% to about 25% Fe₂O₃, from 0% to about 20% CaO, and from 0% toabout 5% MgO.
 37. A cementitious plaster formulation according to anyone of claims 25 to 36, wherein the fly ash particles are generallyspherical, ranging in diameter from 1 to around 45 microns.
 38. Acementitious plaster formulation according to any one of claims 25 to37, wherein the air entraining agent (AEA) is selected from the groupcomprising: nonionic AEAs such as fatty alkanolamides, ethoxylated fattyamines, ethoxylated fatty acids, ethoxylated triglycerides, ethoxylatedalkylphenols, ethoxylated alcohols, alkyl ethoxylates, alkylarylethoxylates; cationic AEAs such as amine ethoxylates and amine oxides;amphoteric AEAs such as betaines; and anionic AEAs such as fatty alkylether sulfates, fatty alkylaryl ether sulfates, alkyl benzenesulfonates, alpha-olefinic-sulfonic acids or salts thereof,sulfosuccinates, and fatty sulfonates.
 39. A cementitious plasterformulation according to any one of claims 25 to 38, wherein the airentraining agent is soluble at a pH range of between 3 and around 6 inorder to ensure solubility in the cementitious mixture.
 40. Acementitious plaster formulation according to claim 39, wherein the airentraining agent, is also soluble at a pH of between 10 and around 11,in order to ensure solubility during the hydration process.